1. Field of the Invention
The present invention is directed in general to impact devices, and, in particular, to a novel propulsion system that allows simple construction with excellent tool attributes, safety, and performance. The benefits of the present propulsion system include a wide range of drive energy, low energy variance, and a high degree of energy level adjustment. The driving device also can be readily used with either a cord connected to traditional electric outlets or can also be powered by batteries or fuel cells.
2. Description of the Related Art
The powered fastening devices presented and discussed here are indirect acting in that they all propel a piston or driver which in turn drives the fastener into the target material. Meanwhile, direct acting tools propel the fastener directlyxe2x80x94no piston or driver is used. Direct acting tools thus require high velocity to achieve the necessary kinetic energy and thus present a dangerous and potentially lethal safety problem. Also, the present invention is directed primarily to hand held tools. Of course, the present device could be mounted in a more elaborate automated, semi-automatic, or robotic system. Also, the present device is primarily directed to driving nails and staples. Variations on the fasteners to be driven or otherwise fixed include corrugated fasteners, screws, hog rings, clips, brads, pins, and the like.
The predominant design for powered fastening driving tools that are currently available are pneumatic. The materials to be joined are generally wood or wood products with attachment materials such as fabrics, plastics, felts, and light gauge metals. The fasteners are generally either nails or staples. In these tools, a piston is propelled by compressed air that is stored in a reservoir contained within the tool and released by a series of valves. The moving piston picks up a fastener from a collated storage magazine and drives the fastener into the target material. A compressed air source is required and is connected to the tool by a hose in order to recharge the reservoir. Pneumatic hand tool drive energy is generally limited to around 120 joules, as the tools get too large and bulky above this level. Energy variance is affected by the variance in air pressure supplied, while energy level adjustment is difficult by means of air pressure adjustment. Instead of pressure adjustment, drive energy is adjusted by mechanical means using an internal driver stop to absorb excess energy.
Powder (or propellant) actuated fastener driving tools are used most frequently for driving fasteners through attachment materials and into hard surfaces such as concrete, masonry, and steel. Many common types of this tool are single fastener, single shot devices; that are, a single fastener is manually inserted into the firing chamber of the tool, along with a single propellant cartridge. After the fastener is discharged, the tool must be manually reloaded with both a fastener and a propellant cartridge in order to be operated again. Examples of this tool are shown in U.S. Pat. Nos. 4,830,254; 4,598,851; and 4,577,793. Some powder actuated tools operate in a manner similar to traditional pneumatic tools in that they contain a magazine which automatically feeds a plurality of fasteners serially to the drive chamber of the tool, while a strip of propellant charges is supplied serially to the tool to drive the fasteners. Examples of this tool are taught in U.S. Pat. Nos. 4,821,938 and No. 4,655,380. Powder actuated tools require expensive cartridges which must be reloaded intermittently. Energy level capability with these tools is high, usually 200 joules and greater. The traditional combustion process cannot readily be run at reduced energy levels, as the reduction methods interfere with the optimum combustion parameters. In addition, drive energy variance increases as energy reduction increases.
Another example of prior art fastener driving tools involves the combustion of gaseous fuel to propel a piston. The combustion gas is stored in a disposable canister mounted on the tool and metered into the combustion chamber by valve means. The gas ignites by an electrical spark and then the expanding combustion products propel a piston, which picks up a fastener from the magazine and drives the fastener into the target material. The practical energy range is similar to pneumatic tools, around 120 joules maximum, as above this range hand held tools tend to get large and bulky. As in powder actuated tools, the combustion process cannot readily be run at reduced energy levels since the known reduction methods interfere with the optimum combustion parameters. Thus, for energy adjustment a mechanical stop means is used to reduce energy levels. An example of this type of prior art tool is U.S. Pat. No. 4,403,722.
Yet another method of propelling fasteners into target materials utilizes an electric motor, a flywheel as energy storage, and various release means. In one example, energy is transferred from the motor to a flywheel storage device. When the flywheel reaches the required rotary speed, and thus energy, a driver is introduced tangentially between the flywheel and an idler roller, and is pinched between the two and rapidly accelerated. The driver then picks up a fastener from the magazine and drives it into the target material by transfer of kinetic energy. One example of this type of prior art tool is shown in U.S. Pat. No. 4,323,127.
In another method that utilizes an electric motor, energy is stored in a flywheel and then released by a conical clutch means that propels a driver via a cable attachment. Fastener driving is the same process as in the other electric motor tool. This device is taught in U.S. Pat. No. 5,320,270. Both electric motor based propulsion systems are highly complex and are difficult to adapt to the rigors of an industrial environment while keeping the weight at a reasonable value for a hand held tool. Energy level control, obtained by controlling the motor speed, is excellent. The energy range attainable can be somewhat greater than pneumatic tools but does not rival powder actuated tools for hand held applications.
Another means for propelling fasteners using hand held tools utilizes a solenoid. Here the driver functions as the rod of the solenoid that is drawn into by the coil and thus propelled. The driver then collides with the fastener and drives it into the target material. Examples of this type of prior art tools are many: one of which is Sears catalog No. 9-27235. In another type of solenoid powered tool, a multistage coil is used. Here a solenoid rod is drawn into the first coil then a switch is engaged which activates a second coil. An example of this type of tool is Chinese Patent No. 2,321,594. There are several limitations to this propulsion system. First, the solenoid system consists of heavy components in both the iron rod and the copper coil windings. The stroke of the solenoid is limited by the electric field of the coil and that, in turn, limits the length of fastener that can be driven. Since solenoids are not energy efficient devices, the energy level is limited to around 30 joules.
Consequently, a need exists for a direct electric propulsion tool as a replacement for traditional combustion (gas or propellant), electric motor, solenoid or pneumatic tools.
It is an object of the present invention to provide a wide range of fastener driving energy that encompasses the sum of the prior art range.
It is further an object of the present invention to provide a simple and rugged design that is suitable for industrial and construction environments from both a survivability and maintainability view.
It is also an object of the present invention to provide a drive energy reduction means that allows the proper drive energy to be adjusted for a wide range of fasteners.
These and other objects of the present invention will be more readily apparent from the description and drawings below.